1. Field of the Invention
The present invention relates to an automatic focusing device of a camera capable of photo-taking in infrared ray.
2. Description of the Prior Art
An imaging lens of a camera usually correct color aberration within a range of a visible ray. Accordingly, in the case of infrared ray photographing, a focal plane is moved behind that for the visible ray. Thus, when an infrared film is loaded in the camera to photograph an object by the infrared ray, it is necessary to move the imaging lens forward by a distance corresponding to a deviation of the focal plane from an in-focus point for the visible ray in order to obtain a sharp image. When the infrared film is loaded in a camera having an automatic focusing device, it is necessary to correct the focusing operation of the imaging lens effected by the automatic focusing device.
When the automatic focusing device having the correction function to the infrared ray is incorporated in a single-lens reflex camera in which an observation image and a photographing image are formed by an imaging lens, the image by the visible ray on a finder is not focused on a pint glass because the imaging lens is moved to focus the image by the infrared ray on the film. Accordingly, a user cannot observe an in-focus object image through the finder.
Further, since the deviation of the focal plane for the infrared ray differs depending on the type of the imaging lens, the exchange of the lens is not permitted in the camera having such a device.